Deep brain stimulation (DBS) and other related procedures involving implantation of electrical stimulation leads within the brain of a patient are increasingly used to treat disorders, such as Parkinson's disease, dystonia, essential tremor, seizure disorders, obesity, depression, restoration of motor control, and other debilitating diseases via electrical stimulation of one or more target sites, including the ventrolateral thalamus, internal segment of globus pallidus, substantia nigra pars reticulate, subthalamic nucleus (STN), or external segment of globus pallidus. DBS has become a prominent treatment option for many disorders, because it is a safe, reversible alternative to lesioning. For example, DBS is the most frequently performed surgical procedure for the treatment of advanced Parkinson's disease. There have been approximately 30,000 patients world-wide that have undergone DBS surgery. Consequently, there is a large population of patients who will benefit from advances in DBS treatment options.
Many of the conditions, diseases and disorders that may be treated with DBS involve irregular brain activity or irregular physiologic activity. For example, tremor activity is associated with Parkinson's disease and other movement disorders. These irregular activities are often indicative of the progression of the condition, disease or disorder.
DBS treatment can also cause side effects. For example, stimulation of the subthalamic nucleus may cause eye movements due to the stimulation spreading to fibers of the oculomotor nerve. An increase in irregular eye movement may be a side effect of over-treatment or may indicate that the stimulation is not being applied to the correct target area.
In current DBS treatment schemes, the parameters of stimulation are set for a patient and remain unchanged for a predetermined amount of time. However, a patient's symptoms may change within that predetermined amount of time, thus subjecting the patient to periods of over-treatment and/or under-treatment. In addition, side effects experienced by the patient may change over time.
Thus, closed-loop DBS systems have been developed, or at least conceived, wherein stimulation parameters are adjusted in response to a sensed condition. For example, a positive closed-loop DBS system may be configured for sensing seizure or tremor activity using, e.g., EEG, and for applying stimulation energy in order to prevent or mitigate the seizure or tremor activity. In another example, a DBS system may be configured for sensing eyelid movement using, e.g., EMG, and for adjusting stimulation parameters in order to provide optimal control of irregular eyelid movement. When operating DBS systems (whether closed-loop or open-loop) within patients, the same stimulation used to efficaciously treat the neurological disorders from which the patients suffer may also cause side-effects, such as uncontrolled eyeball movement.
There, thus, remains a need for a DBS system that prevents or otherwise mitigates side-effects that may occur during treatment of neurological disorders, while retaining the efficacy of the treatment.